Field of the Invention
The invention relates to a method for cleaning diesel engine exhaust gas. It is known that the combustion of diesel fuel leads to the formation of a large number of different pollutants and hydrocarbon-enriched soot particles (referred to below as particles for short), which are removed or at least reduced by suitable catalytic converters with active materials which have a specific action and with separate particle filters. Furthermore, if SCR catalytic converters are used, a device that can be used to meter a reducing agent into the exhaust-gas stream is required. For example, Published, European Patent Application EP 0 341 832 A2 describes a method for cleaning diesel engine exhaust gases in which a device with a platinum-containing catalytic converter is combined with a device for filtering out particles. Furthermore, adsorbers that adsorb pollutants in the lower temperature range and desorb them again at elevated temperatures are frequently used.
It is accordingly an object of the invention to provide a method for cleaning diesel engine exhaust gas that overcomes the above-mentioned disadvantages of the prior art methods of this general type, which is simplified in terms of the outlay on equipment.
With the foregoing and other objects in view there is provided, in accordance with the invention, a method for cleaning diesel engine exhaust gas. The method includes the steps of metering a reducing agent suitable for reducing nitrogen oxides into an exhaust-gas stream upstream of a catalytic converter; and
passing the exhaust gas through the catalytic converter having an active material composed (in % by weight) of:
In accordance with an added feature of the invention, the active material has a BET surface area of 40-150 m2/g.
In accordance with an additional feature of the invention, the active material has a pore volume measured using a Hg penetration method of 200-600 mm3/g.
In accordance with another feature of the invention, the active material has a monomodal pore radius distribution, a frequency maxima of a pore radii lying in a range of 5-10,000 nm.
In accordance with a further feature of the invention, there is the step of using TiO2 in its anatase modification.
In accordance with a concomitant feature of the invention, the active material has a polymodal pore radius distribution, a frequency maxima of a pore radii lying in a range of 5-10,000 nm.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is described herein as embodied in a method for cleaning diesel engine exhaust gas, it is nevertheless not intended to be limited to the details described, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.